High-frequency interstage coupling device



April 9, 1935.

A. CROSSLEY El" AL HIGH FREQUENCY INTERSTAGE COUPLING DEVICE Filed April 10, 1954 v IN VENT 0R5, ALF/8E0 CROSSLEX BYHERBERT 5 ME/NEMA,

ATTORNEY.

' Patented Apr. '9, 1935 UNITED STATES HIGH-FREQUENCY INTERSTAGE COUPLING DEVICE Alfred Crossley and Herbert E. Meinema, Chicago, 111., assignors to Johnson Laboratories, Inc., Chicago, 111., a corporation of Illinois Application April Ill, 1934, Serial No. 719,904

6 Claims.

This invention relates broadly to improvements in high-frequency amplifying systems, and more particularly to systems designed to be operated at frequencies of about 150 kilocycles and upwards, such for example as those in the highfrequency amplifiers of radio receivers. Such systems, in general, include in addition to the amplifying thermionic relay, a resonant system consisting of two inductance coils arranged in 10 magneticrelation to each other, one of the coils being shunted by a variable condenser. The condenser is normally of a type having very low losses, and therefore the emciency of the complete design depends to a very large extent upon the inductance coils.

A principal object of this invention is to provide a novel type of coupling means for use in such an amplifying system, which, because of its design, will greatly increase the eficiency of the system. This object is attained in part by using iron-cored inductances having new and highly desirable attributes. The cores which we use in these inductances are term-magnetic and consist of finely-divided individually-insulated iron particles compressed with a binding material to make a core body. Qores of this type, suitable for use at high frequencies, are disclosed in British Patents Nos. 366,475 and 403,368 and have recently been describedin numerous publications in the United States and abroad.

The combination of such a core with a suitable winding is to be designed in accordance with Patent No. 1,978,568, issued Oct. 30, 1934, for Improved high-frequency inductance. The inductance consists essentially of a tubular cylindrical core of the type described, with a pancake universal winding at its center, the length of the winding being usually from three-eighths to twothirds of the radial depth, the length of the core being from 2 to 5 times the length of the winding.

Still a further object of the invention is attained by so fashioning the insulating frame or support on which the inductance coils and their cores are mounted that it will constitute a single and integral entity embodying all of the features which are essential to admit of the mounting of the cores and their coils thereon, as well as to enable the frame or support to be itself mounted on an adjacent part of the structure. Furthermore, the frame may include elements for accurately holding the leads in predetermined relative positions in order that the spacing of said leads will be definitely established.

Inductances of the class here contemplated normally occur in pairs, one coil being connected in the output circuit of a first thermionic relay, and. the other coil being connected in the input circuit of a second thermionic relay. In order to transfer energy from the first circuit to the second, the coils may be coupled magnetically and thus form a transformer, or they may be coupled capacitively by means of a small condenser connecting their high-potential ends, or a combination of magnetic and capacitive coupling may be used in order to obtain more uniform gain over the desired band of frequencies. The coil in the output'circuit of the first thermionic relay is usually called the primary, and the coil in the input circuit of the second thermionic relay is usually called the secondary. In some instances, however, these designations may be reversed, and either of the thermionic relays may in certain types of apparatus be arranged so that it does not operate strictly as an amplifier. These variations, however, are not material with respect to the application and scope of the present invention. The variable tuning condenser is usually shunted across the coil here designated as the secondary coil.

In present-day designs, coupling devices of the class here under consideration normally employ two magnetically-coupled air-core inductances. By suitably designing the primary and secondary windings and by adjustment of the tuning condenser, the system may be tuned to be resonant at the desired frequency. In order to effect a maximum transfer of energy between the primary and the secondary, it is essential that the magnetic coupling between the two windings shall be closely of the optimum value. In the present designs, it is normal to establish the degree of coupling in the design of the transformer, so that when the coils are assembled the proper coupling will exist.

Because of the losses which normally exist in air-core coils of the type now commonly used, it is not essential to provide means for adjusting the coupling between the primary and secondary coils after the unit is assembled. It isusually sufiicient to determine experimentally what physical relation between the two coils will give'approximately the correct coupling and then to mechanically design the transformer so as to produce this relation.

In the designs herein described, the losses in the coils themselves are greatly decreased, and it therefore becomes desirable to provide means for accurately adjusting each coupling device to the desired coupling between primary and secondary. The present invention, therefore, includes designs employing coils having greatly increased efliciency, and arrangements whereby two such coils may be magnetically related in a coupling device withmeans for producing an accurate adjustment of the magnetic coupling between the windings. It is also possible to provide an adjustment, as hereinafter explained, whereby the magnetic coupling adds to the capacitive coupling.

Additionally, it is possible to so adjust the transformers of the present invention that there is substantially no magnetic coupling between the primary and secondary, that is, the magnetic coupling is zero and the coupling between the circuits is entirely capacitive. Heretofore, in circuits where it was desired to have no magnetic coupling between two inductances which would otherwise constitute the primary and the secondary of a magnetically-coupled transformer,

it has been necessary to surround each of the windings by a separate electro-magnetic shield.

Because of,the higher efficiency of iron-core coils, it is possible to obtain greater energy transfer with less coupling than is permissible with air-core coils. This results in an increase in the electrical efiiciency of the coupling device. For example, one embodiment of the invention uses about 8% magnetic coupling between the coils and a coupling condenser of micromicrofarads. An alternate form uses zero magnetic coupling and a coupling condenser of micromicrofarads. Either of these coupling devices will give substantially twice the amplificationwhile maintaining the selectivity the same-as it would be with air-core coils. The invention will be better understood by reference to the accompanying drawing, which is illustrative of one possible mechanical embodiment of the invention and in which- Fig. 1 is an elevation of a high-frequency coupling device employing ferro-magnetic core bodies;

Fig. 2 is a bottom view of the coupling device shown in Fig. 1;

Fig. 3 is a view in perspective of the supporting frame for the coupling device elements;

Fig. 4 presents a simplified schematic wiring diagram which illustrates a method of employing the coupling device of this invention in the circuits of a high-frequency amplifier, and

Fig. 5 shows a slight modification of the frame disclosed in Fig. 3.

Referring to Fig. 1, the coupling device here illustrated consists of an insulating frame I, preferably of a phenolic compound such as bakelite molded in one piece, in order to avoid the cost of assembling operations which would be necessary if it included, as it might, a plurality of elements. The frame I is designed to be conveniently secured to the receiver chassis 2 by means of the threaded mounting studs 3, which an: zreferably molded into the frame I, and nu s The frame I comprises parallel side bars 5,

united by a cross bar 6, and provided with grooves I in certain of which the leads I4 from the coils may be secured by any suitable cementitious substance. It is desirable that they be held in fixed relation to the frame so that their relative positions are maintained. One of the grooves I may carry a lead-22 from the high-potential terminal I3 of the secondary coil upward, to be more conveniently attached to the grid 'cap terminal on an associated thermionic relay.

The cross bar 6 sustains the coil 8, and may be provided with an integral fixed stud Ba, extending into and cemented to the hollow cylindrical core 9 of the coil 8.

Theframe I carries a wood or molded guide rod Ill, freely extending through the hollow cylindrical core II of the coil I2, to thereby permit the core I I and the coil I2 to be moved relatively to the center of the magnetic system. This adjustment of the core II and the coil I2 might, however, be attained if said guide rod Ill were longitudinally movable and said core and said coil were fixed thereto as shown in .Fig. 5.

The coils 8 and I2 constitute the primary and secondary, respectively, of the coupling device. The coils are preferably of the type produced on a universal winding machine and are designed to have a desirable relation of length to depth of winding. For use in the band of frequencies between 550 and 1500 kilooycles, the primary coil 8 may have an inductance of "about 3.2 millihenries, and be resonant at a frequency below the desired band of frequencies, thereby producing the minimum effect on the gain within the desired band of frequencies' It may be wound with number 36 solid single silk covered enameled wire. The secondary coil I2 may be wound with Litzendraht wire consisting of ten strands of number 41 enameled wire, and may have an inductance of about 250 microhenries so as to cover the desired band of frequencies when tuned by a variable condenser having a maximum capacity of about 365 micromicrofarads. The coils 8 and I2 are secured to the cores 9 and II, respectively, by means of any suitable cement.

In the embodiment here shown, it will be noted that the core 9 of the primary coil 8 is smaller than the core II of the secondary coil I2. Since the secondary coil is a component of a tuned circuit, it is desirable to keep its losses as low as possible. l-Ience a relatively small coil on a relatively large core is used. The primary coil, however, is untuned, and its losses may be higher without serious effect. economy a relatively large coil on a relatively small core is used. This choice may be found advantageous in those cases where cost is an important consideration. 7

Referring to Figs. 1 and 2, terminals I3 extend outward from the frame I, being preferably eyeletted through square holes in the frame I. Leads I4 from the coils 8 and I2 extend to the terminals I3, either directly from the coils or secured in the grooves I in the frame I. The leads It may be soldered or attached by other suitable means to the terminals I3. Coupling condenser I5 is mounted as shown relative to the frame I by soldering itfto the two terminals I3 which connect to the high-potential ends of the coils 8 and I2. For operation in the frequency hand between 550 and 1500 kilooycles, this condenser may have a capacity of 25 micromicrofarads, in which case zero magnetic coupling may be used; or it may have a capacity of 15 micromicrofarads in conjunction with about 8% magnetic coupling.

-In general, different values of capacitive or magnetic coupling, or combinations of both, can be used to adapt the design to the individual requirements of a particular piece of receiving apparatus,

Referring again to Fig. 1, the assembly may include a metal shield I6 which is usually desirable in order to prevent electro-magnetic and electrostatic coupling between adjacent coupling devices. The shield It may be arranged to be eye- Hence for the sake of terminals.

, 1,997,453 letted to the chassis 2 as shown, or otherwise suitably fixed in place. It should be provided with a hole 23 to receive the control-grid lead 22 from a thermionic relay. The metal chassis 2 of the receiver completes the shielding of the coupling device.

Fig. 3 servesto make clear a preferred construction of the molded insulating frame I. The small extensions la for the terminals 13 are arranged to readily permit eyeletting of the terminals in place. The extensions adjacent the sides of the frame receive the high-potential terminals of the primary and secondary respectively, and the centrally located extensions on the opposite side of the frame receive the low-potential Fig. 4 shows a coupling device of the type herein contemplated connected between the output circuit ll of the thermionic relay l8 and the input circuit l9 of the thermionic relay 28. The primary coil 8 is connected in series with the anode and cathode of the thermionic relay l8.

It will be observed that the coils 8 and, 12 are mutually at right angles and that the cores 9 and H are also mutually at right angles. It will be clear that by positioning the coil 12 and the core II at what may be designated as the magnetic center of the magnetic system comprising the cores 9, II, and the coils 8, l2, there will be no magnetic coupling whatever between the coils 8 and 12, or at least only a very small degree of coupling. However, by shifting the coil l2 and the core I l longitudinally along its guide rod H), a degree of coupling of a substantial order and adequate for the purpose of the'design can be secured. The advantage of the arrangement lies in the fact that it is possible to quickly obtain in production any desirable degree of coupling with only a small movement of the coil I2 and the core H. A possible adjusted position of the coil l2 and the core H is indicated by the dotted outline in Figure 1. After the coil I2 and the core I I have been adjusted to the position producing the desired degree of coupling, they are securely cemented in place.

Capacitive coupling or a combination of capacitive and magnetic coupling is often desirable in coupling devices designed for use over' a band of frequencies, since it is often possible to materially improve the uniformity of gain and selectivity which is obtained over the band of frequencies by a proper choice of the coupling,

means. Capacitive coupling between the primary and secondary circuits is obtained by means of thecondenser IS. The desired degree of magnetic coupling, within a range from zero to a substantial order, is readily obtained by adjustment of the position of the coil l2 and the core II. If desired, the magnetic coupling can be made to aid the capacitive coupling by moving the coil 12 and the core I I in the opposite direction from the zero coupling position.

Certain specific design data and constants have been given to complete the description of the present invention. It should be understood, however, that time constants are mentioned merely by way of example in describing certain specific embodiments which in practice have proved satisfactory, and are not intended to suggest any specific limitations as. to the scope of this invention.

Having thus described our invention, what we a frame, two compressed comminuted tubular ferro-magnetic cores mounted mutually at right angles upon said frame, aconcentrated primary winding wound on one of said cores, a concentrated secondary winding wound upon the other of said cores, said primary winding having a natural frequency lower than any frequency to which said secondary winding is intended to be tuned.

3. A high-frequency coupling device comprising primary and secondary structures mounted mutually at right angles upon an insulating frame, said primary and secondary structures each consisting of a concentrated winding wound upon a compressed comminuted tubular ferromagnetic core, means whereby the electro-magnetic coupling between said windings may be adjusted to any desired small value, said primary having a natural frequency lower than any frequency to which said secondary winding is intended to be tuned.

4. A frame for a high-frequency transformer, said frame having upstanding elements, a cross bar uniting said upstanding elements and having means for sustaining a magnetic core,,widelyspaced means for supporting a pair of highpotential terminals, and adiacent means for supporting a pair of low-potential terminals.

5. An insulating frame for supporting the ferro-magnetic cores, the leads to the windings, and the terminals for the leads of a high-frequency transformer, said frame having two upstanding elements united by a cross bar, an upwardly extending post upon said cross bar for supporting one of said cores, perforated flanges extending downwardly from said cross bar adjacent said upstanding elements for supporting the high-potential terminals of said transformer, perforated flanges extending downwardly centrally of said cross bar for supporting the lowpotential terminals of said transformer, and grooves in said upstanding elements for supporting the leads from the terminals to the windings of said transformer.

6. A moulded insulating frame for a high-frequency transformer, said frame having upstanding elementswhich serve as spacingmeans for the leads of said transformer, and a cross bar for fixedly uniting said upstanding elements, said cross bar carrying perforated flanges for supporting terminals for said leads.

ALFRED CROSSLEY. HERBERT E. MEINEMA. 

